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  • 1
    Electronic Resource
    Electronic Resource
    Altered islet Beta-cell function before the onset of Type 1 (insulin-dependent) diabetes mellitus (1992)
    Springer
    Diabetologia 35 (1992), S. 277-282 
    Details
    ISSN: 1432-0428
    Keywords: Identical twins ; Type 1 (insulin-dependent) diabetes mellitus ; intravenous glucose ; insulin response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To define the glucose to insulin dose-response relationship before the onset of diabetes, we studied 22 nondiabetic co-twins of patients with Type 1 (insulin-dependent) diabetes mellitus and nine control subjects. All had intravenous glucose tests at 0.02, 0.1 and 0.5 g/kg and were followedup prospectively for at least 6 years. Seven twins developed diabetes a mean of 7 months later; the remaining 15 are now unlikely to develop diabetes. The seven pre-diabetic twins had higher fasting insulin levels than control subjects (4.2±2.0 vs 1.8±1.8 nmol/l; p〈0.05); but lower glucose clearance (1.0±0.5 vs 1.9±0.7 %/min; p〈0.05), first phase insulin response at 0.5 g/kg (21.1±23.2 vs 143±50 nmol/l; p〈0.0001), and total insulin responses at 0.1 g/kg (p〈0.05) and 0.5 g/kg (p〈0.00005). Using a curve-fitting programme, the normal glucose to insulin relationship was lost in prediabetic twins who had lower coefficient of determination (R2) than control subjects (p〈0.01). In contrast, 15 low-risk twins and their nine control subjects had similar fasting glucose and insulin levels, glucose clearance, R2 and insulin secretory responses to different glucose loads. The positive predictive values of subnormal R2 and subnormal first phase insulin response were 67 % and 58 % respectively. These observations demonstrate an altered glucose to insulin dose-response relationship and loss of maximum insulin secretory response to glucose before the onset of Type 1 diabetes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400930
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  • 2
    Electronic Resource
    Electronic Resource
    Impaired glucose tolerance precedes but does not predict insulin-dependent diabetes mellitus: a study of identical twins (1990)
    Springer
    Diabetologia 33 (1990), S. 497-502 
    Details
    ISSN: 1432-0428
    Keywords: Impaired glucose tolerance ; pre-diabetes ; insulin-dependent diabetes ; identical twins ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Non-diabetic identical twins of insulin-dependent diabetic patients were studied within five years of the diagnosis of their index twin in order to determine whether changes in intermediary metabolism precede the onset of insulin-dependent diabetes mellitus. Two studies were performed: a cross-sectional study of 12 non-diabetic twins and a prospective study of a separate group of 41 non-diabetic twins. Ofthe 12 twins tested in the cross-sectional study six developed insulin-dependent diabetes and six did not; the six who developed diabetes were given an oral glucose load a mean of 10 months before diagnosis; they then had normal fasting blood glucose levels but worse glucose tolerance than control subjects (120 min post-load (mean±SD) blood glucose 8.5±3.5 vs 4.9±0.9 mmol/l respectively, p〈0.05). However, blood lactate, pyruvate, alanine, glycerol, 3-hydroxybutyrate and serum insulin levels were similar. In contrast, the six twins in this cross-sectional study who did not develop diabetes and are now unlikely to do so, as a group, had no significant changes compared with the control subjects though one had impaired glucose tolerance. To determine the predictive value of impaired glucose tolerance a separate group of 41 non-diabetic twins was studied prospectively for 8 to 22 years having a total of 147 glucose tolerance tests in this period; in this group six developed diabetes. Eight of the 41 had impaired glucose tolerance; impaired glucose tolerance was found in four of the six who developed diabetes as compared with only four of the 35 who did not (p〈0.01). Impaired glucose tolerance in these non-diabetic identical twins had a positive predictive value of33% for developing diabetes. The four twins with impaired glucose tolerance who remain nondiabetic now have normal glucose tolerance. We conclude that impaired glucose tolerance may precede the onset of insulin-dependent diabetes mellitus by many months but the change does not specifically predict the disease even in identical twins of diabetic patients. These observations are consistent with the possibility that in some twins the disease process can occur yet remit without leading to diabetes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405112
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  • 3
    Electronic Resource
    Electronic Resource
    Photosynthesis in air and in water of Acanthophora najadiformis growing within a narrow zone of the intertidal (1993)
    Springer
    Marine biology 117 (1993), S. 133-138 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this work, we investigated photosynthetic gas exchange responses of the red alga Acanthophora najadiformis (collected in 1991 from a shore near Netanya, Israel) to heating, light, inorganic carbon and desiccation of the thalli. This was done to elucidate some of the contributing causes for its particular restricted vertical distribution within the lower intertidal zone of the Israeli Mediterranean rocky shore. In contrast to other common intertidal species, the photosynthetic performance of A. najadiformis was very sensitive to desiccation and to high temperature, and these factors may thus prevent the alga from growing above the surge zone. On the other hand, this species photosynthesized five times faster in air than in water (provided it was kept highly hydrated), and this may be the reason why it does not succeed in competing with other algae in the subtidal which use HCO 3 - more efficiently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346435
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  • 4
    Electronic Resource
    Electronic Resource
    Use of pulse amplitude modulated (PAM) fluorometry for in situ measurements of photosynthesis in two Red Sea faviid corals (1998)
    Springer
    Marine biology 131 (1998), S. 607-612 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Measurements of the photosynthetic activity of symbiotic zooxanthellae in corals under natural growth conditions has been limited until recently, and this is one of the first reports on utilising a newly developed underwater pulse amplitude modulated (PAM) fluorometer (the Diving-PAM, Walz Gmbh, Germany) for such studies in situ. Photosynthetic responses to irradiance (photosynthetic photon flux, PPF) of the two faviid corals Favia favus (Forskål) and Platygyra lamellina (Ehrenberg) were measured while snorkelling or SCUBA diving (in August 1997), and we report here the results in terms of effective quantum yields of photosystem II (Y ) and estimated rates of photosynthetic electron transport (ETR, calculated as Y × 0.5 × PPF × FA, where FA is the estimated fraction of light absorbed by the photosymbiont-containing tissue). Both species showed a reduction in Y with increasing actinic irradiances produced by the instrument above 500 μmol photons m−2 s−1, and the corresponding ETR values yielded apparently typical photosynthesis versus irradiance (P-I ) curves, which saturated between 1500 and 2000 μmol photons m−2 s−1. It was found that 30 s irradiation at each PPF level was sufficient to give optimal ETR values and, therefore, each P-I curve could be obtained within a few minutes. In situ point measurements from various areas of colonies under ambient light showed average ETR values within the range expected from the P-I curves. In order to test the Diving-PAM in an eco-physiologically relevant experiment, photosynthetic ETR versus PPF was measured for three sections of a large P. lamellina, each section of which received different natural irradiance levels. The results clearly demonstrated adaptations to the ambient light field in that vertical and downward-facing portions of the colony showed gradually lower maximal ETRs, steeper initial slopes of the P-I curves and, accordingly, lower light saturation points than upward-facing areas receiving higher light levels. Based on these trials, some evaluations are given as to the applicability of the Diving-PAM for photosynthetic measurements when monitoring similar corals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050352
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  • 5
    Electronic Resource
    Electronic Resource
    In situ measurements of photosynthetic irradiance responses of two Red Sea sponges growing under dim light conditions (1998)
    Springer
    Marine biology 131 (1998), S. 613-617 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic responses to irradiance by the photosymbionts of the two Red Sea sponges Theonella swinhoei (Gray) and Clionavastifica (Hancock) growing under dim light conditions were measured in situ (in September 1997) using a newly developed underwater pulse amplitude modulated (PAM) fluorometer. Relative rates of photosynthetic electron transport (ETR) were calculated as the effective quantum yield of photosystem II (Y ) multiplied with the photosynthetic photon flux (PPF). Photosynthesis versus irradiance (P-I ) curves, obtained within minutes, showed that individual specimens of both sponges, growing under very low light conditions, feature lower light saturation points as well as lower maximal ETRs than individuals growing under higher light. Evaluations of such curves using low irradiances of the actinic light source (20 to 130 μmol photons m−2 s−1) showed a general decrease in Y, with a shoulder from the lowest irradiance applied till 20 to 30 μmol photons m−2 s−1. Point measurements yielded ETRs close to what could be estimated from the P-I curves. These point measurements also revealed good correlations between the diurnally changing ambient irradiances (1 to 50 μmol photons m−2 s−1) and average ETR values for both species. Further analysis showed that although Y values varied considerably between the different point measurements, they did not decrease significantly with light under these very low irradiances. Therefore, PPF rather than Y seems to determine the in situ diel photosynthetic performance at the low ambient irradiances experienced by these sponges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050353
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  • 6
    Electronic Resource
    Electronic Resource
    Photosynthetic carbon acquisition in the red algaGracilaria conferta (1991)
    Springer
    Marine biology 110 (1991), S. 195-198 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic properties of the common red algaGracilaria conferta, collected from the eastern Mediterranean Sea were investigated in 1989, in order to begin evaluating its adaptative strategies with regard to the inorganic carbon composition of seawater, and to test whether the alleged C4 photosynthesis of anotherGracilaria species is common within the genus. Net photosynthetic rates ofG. conferta were, under ambient conditions of inorganic carbon (ca. 10µM, CO2 and 2.2 mM HCO 3 - ), not sensitive to O2 over the range 10 to 300µM, and the CO2 compensation point was low (ca. 0.005µM). Ribulose-1,5-bisphosphate carboxylase/oxygenase was the major carboxylating enzyme, with a crude extract activity of 175µmol CO2 g−1 fresh wt h−1 while phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase were present at 70 and 20%, respectively, of that activity. No activities of the decarboxylases NAD-and NADP-malic enzyme could be detected. The14C pulse-chase incorporation pattern showed thatG. conferta fixes inorganic carbon via the photosynthetic carbon reduction cycle only, with no evidence for photosynthetic C4 acid metabolism. Photosynthesis at the natural seawater pH of 8.2 was, at 25°C and saturating light, saturated at the ambient inorganic carbon concentration of 2.5 mM. It is proposed that, under ambient inorganic carbon conditions, a CO2 concentrating system other than C4 metabolism provides an internal CO2 concentration sufficient to suppress the O2 effect on ribulose-1,5-bisphosphate carboxylase/oxygenase and, thus, on photorespiration, in a medium where the external free CO2 concentration is lower than theK m(CO2) of the carboxylating enzyme. Since inorganic carbon, under natural saturating light conditions, seems not to be a limiting factor for photosynthesis ofG. conferta, it likely follows that other nutrients limit the growth of this alga in nature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313704
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  • 7
    Electronic Resource
    Electronic Resource
    Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa (1997)
    Springer
    Marine biology 129 (1997), S. 363-366 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural seawater (2.1 mM, mostly in the form of HCO3 −), and they exhibited more than three time higher rates at inorganic carbon saturation (〉6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K 1/2 = ca. 2.5 mM), followed by the subtidal species (K 1/2 〉 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was 〉50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular HCO3 − dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO2 concentration which remained in the closed experimental systems at that pH, pointing toward HCO3 − uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO3 − directly, since this is a more efficient way of HCO3 − utilisation than extracellular HCO3 − dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO2 levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050176
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  • 8
    Electronic Resource
    Electronic Resource
    Photosynthetic carbon acquisition in the red alga Gracilaria conferta (1992)
    Springer
    Marine biology 112 (1992), S. 697-700 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this continuing study on photosynthesis of the marine red alga Gracilaria conferta, it was found that ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in crude extracts had a K m (CO2) of 85 μM. Since seawater contains only ca. 10 μM CO2, it appears that this alga must possess a CO2 concetrating system in order to supply sufficient CO2 to the vicinity of the enzyme. Because this species is a C3 plant (and thus lacks the C4 system for concentrating CO2), but can utilize HCO3 - as an exogenous carbon source, we examined whether HCO3 - uptake could be the initial step of such a CO2 concetrating system. The surface pH of G. conferta thalli was 9.4 during photosynthesis. At this pH, estimated maximal uncatalyzed HCO3 - dehydration (CO2 formation) within the unstirred layer was too slow to account for measured phostosynthetic rates, even in the presence of an external carbonic anhydrase inhibitor. This observation, and the marked pH increase in the unstirred layer following the onset of light, suggests that a HCO3 - transport system (probably coupled to transmembrane H+/OH- fluxes) operates at the plasmalemma level. The involvement of surface-bound carbonic anhydrase in such a system remains, however, obscure. The apparent need of marine macroalgae such as G. conferta for CO2 concentrating mechanisms is discussed with regard to their low affinity of Rubisco to CO2 and the low rate of CO2 supply in water. The close similarity between rates of Rubisco carboxylation and measured photosynthesis further suggests that the carboxylase activity, rather than inorganic carbon transport and intercoversion events, could be an internal limiting factor for photosynthetic rates of G. conferta.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346189
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  • 9
    Electronic Resource
    Electronic Resource
    Photosynthetic utilisation of carbon and light by two tropical seagrass species as measured in situ (2000)
    Springer
    Marine biology 137 (2000), S. 755-761 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In situ measurements of seagrass photosynthesis in relation to inorganic carbon (Ci) availability, increased pH and an inhibitor of extracellular carbonic anhydrase were made using an underwater pulse amplitude modulated (PAM) fluorometer. By combining the instrument with a specially designed Perspex chamber, we were able to alter the water surrounding a leaf without removing it from the growing plant. Responses to Ci within the chamber showed that subtidal plants of the seagrasses Cymodocea serrulata and Halophila ovalis had photosynthetic rates that were limited by the ambient Ci concentration depending on the irradiance that was available during short-term photosynthesis–irradiance trials. Relative electron transport rates (RETRs) at light saturation (up to 500 μ mol photons m−2 s−1) increased by 66–100% when the Ci concentration was increased from ca. 2.2 to 6.2 mM. On the other hand, intertidal plants of the same species exhibited a much lesser limitation of photosynthesis by Ci at any irradiance (up to 1500 μ mol photons m−2 s−1). Both species were able to use HCO− 3 efficiently, and there was stronger evidence for direct uptake of HCO− 3 rather than extracellular dehydration of HCO− 3 to CO2 prior to Ci uptake. Subtidally, H. ovalis and C. serrulata grew to 10 and 12 m, respectively, where ambient irradiances were approximately 16 and 11% of those at the surface. Maximum RETRs (at light saturation) were lower for these deep-growing plants than for the intertidally growing ones. For both species, the onset of light saturation of photosynthesis (E k) occurred at approximately 100 μ mol photons m−2 s−1 for the deep water populations, which was four and two times lower than for the shallow populations of C. serrulata and H. ovalis, respectively. This, and the differences in maximal photosynthetic rates (RETR max), reflects an acclimation of the deep-growing populations to the lower light environment. The results presented here show that photosynthesis, as measured in situ, was limited by the availability of Ci for the deeper growing plants in Zanzibar, while the intertidally growing plants photosynthesised at close to Ci saturation. The latter result is contrary to previous conclusions regarding Ci limitations for these intertidal plants, and, in general, our findings highlight the need for performing similar experiments in situ rather than under laboratory conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270000433
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  • 10
    Electronic Resource
    Electronic Resource
    Detection of anterior horn lesions by MRI in central European tick-borne encephalomyelitis (1999)
    Springer
    Journal of neurology 246 (1999), S. 1169-1171 
    Details
    ISSN: 1432-1459
    Keywords: Key words European tick-borne encephalitis ; Magnetic resonance imaging ; Central nervous system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report a case of central European tick-borne encephalitis with cervical myelitis presenting clinically as a lower motor neuron syndrome of the upper limbs with proximal asymmetrical pareses and atrophies. There were no sensory deficits nor signs of lesions of the spinal pathways or signs of encephalitis or meningitis. The affected motor fibers of the upper limbs were electrically inexcitable, but sensory findings were normal. Electromyography of the paralyzed muscles revealed pathological denervation activity without voluntary activation. The initial magnetic resonance imaging (MRI) showed a large hyperdense lesion in the anterior part of the cervical cord from C3 to T1. Despite the fact that MRI changes disappeared completely within 6 weeks the patient showed only little improvement in the paralyzed muscles after 6 months. To our knowledge, these MRI changes in patients with tick-borne encephalitis, consistent with an isolated anterior horn lesion, have never been reported previously. The course may have been aggravated by an initial antibiotic treatment with cephalosporins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050537
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